1. Field of the Invention
The present invention relates to a novel test device for detecting an analyte in a test sample by means of a binding assay. In particular, this invention relates to a novel test device incorporating mobile control reagents.
2. Description of Related Art
The ability to use materials which specifically bind to an analyte of interest has provided a means for developing diagnostic devices based on the use of binding assays. Binding assays incorporate specific binding members, typified by antibody and antigen immunoreactants, wherein one member of the specific binding pair is labeled with a signal-producing compound (e.g., an antibody labeled with an enzyme, a fluorescent compound, a chemiluminescent compound, a radioactive isotope, a direct visual label, etc.). For example, in a binding assay the test sample suspected of containing analyte can be mixed with a labeled reagent, e.g., labeled anti-analyte antibody, and incubated for a period of time sufficient for the immunoreaction to occur. The reaction mixture is subsequently analyzed to detect either that label which is associated with an analyte/labeled reagent complex (bound labeled reagent) or that label which is not complexed with analyte (free labeled reagent). As a result, the amount of free or bound label can be correlated to the amount of analyte in the test sample.
The solid phase assay format is a commonly used binding assay technique. There are a number of assay devices and procedures wherein the presence of an analyte is indicated by the analyte""s capacity to bind to a labeled reagent and an immobilized or insoluble complementary binding member. The immobilized binding member is bound, or becomes bound during the assay, to a solid phase such as a dipstick, teststrip, flow-through pad, paper, fiber matrix or other suitable solid phase material. The binding reaction between the analyte and the assay reagents results in a partitioning of the labeled reagent between that which is immobilized upon the solid phase and that which remains free. The presence or amount of analyte in a test sample is typically indicated by the extent to which the labeled reagent becomes immobilized upon the solid phase material.
The use of reagent-impregnated teststrips in specific binding assays is well-known. (See, eg. Deutsch, et al. U.S. Pat. No. 4,361,537, and Brown, III et al. U.S. Pat. No. 5,160,701). In such procedures, a test sample is applied to one portion of the teststrip and is allowed to migrate or wick through the strip material. Thus, the analyte to be detected or measured passes through or along the material, possibly with the aid of an eluting solvent which can be the test sample itself or a separately added solution. The analyte migrates into or through a capture or detection zone on the teststrip, wherein a complementary binding member to the analyte is immobilized. The extent to which the analyte becomes bound in the detection zone can be determined with the aid of the labeled reagent which can also be incorporated in the teststrip or which can be applied separately.
In general, teststrips involve a material capable of transporting a solution by capillary action, i.e., a wicking or chromatographic action as exemplified in Gordon et al. U.S. Pat. No. 4,956,302. Different areas or zones in the teststrip contain the assay reagents needed to produce a detectable signal as the analyte is transported to or through such zones. The device is suited for both chemical assays and binding assays and uses a developer solution to transport analyte along the strip.
To verify the stability and the efficacy of the assay reagents needed to produce the detectable signal, existing assays typically require that one or more strips from each manufacturing lot be separately assayed for both positive and negative controls. For the positive control, this typically requires a solution xe2x80x98spikedxe2x80x99 with the analyte of interest which is applied to the strip and developed as described above. A negative control will use a xe2x80x98blankxe2x80x99 sample, that is, one which has no analyte present. However, these methods require the use of separate strips which are not controlling for device specific variations in procedure or reagents, and are not developed under the actual assay conditions, i.e., in the presence of a patient sample. Furthermore, the need for parallel testing of controls significantly increases the cost of performing diagnostic assays.
Another disadvantage of conventional teststrip devices having control reagents is that the controls fail to exactly mimic the reaction of a patient sample with the teststrip reagents. For example, in teststrip devices utilizing a sandwich assay format, an analyte is first reacted with a labeled binding reagent to form a complex which then becomes bound to a detection site on the device via a second binding reagent. Although certain control reagents provided in these devices control for one portion of the total patient sample reaction, such as the binding of labeled reagent to the analyte, no control is provided to verify the second portion of the patient sample reaction, i.e. the binding of the labeled complex to the binding reagent at the detection site. The failure of either of these binding reactions to occur leads to the erroneous conclusion of a negative patient sample. Thus, there is a need for specific control reagents which permit the simultaneous confirmation of the assay results by mimicking the entire patient reaction.
The invention provides, in an analytical device for determining the presence or amount of an analyte in a test sample, having a strip with a proximal end and a distal end, wherein the test sample can travel from the proximal end to about the distal end by capillary action, and wherein the strip contains an immobilized patient capture reagent which binds to a member selected from the group consisting of the analyte, an ancillary specific binding member and a labeled reagent,
the improvement comprising:
a) a mobile positive control reagent;
b) an immobilized positive control capture reagent that is located downstream from the mobile positive control reagent and is capable of binding the mobile positive control reagent.
The invention also provides an immobilized negative control reagent used to determine the presence of non-specific binding or aggregation of any labeled reagent in the device at a site independent of the positive control reagent and positive control capture reagent.
The test kits of the present invention contain the analytical device and may include additional instructions and/or ancillary reagents such as diluents and buffers.